The project objective is continued development of sequence-specific blocking agents for nucleic acids. Such compounds when combined with an appropriate polynucleotide targeting vector allow specific blockage of any desired sequence in RNA or DNA. A variety of compounds will be tested to determine agents providing the best efficiency and specificity of gene blockage. Much of the testing of these agents will be the plasmid, pBR322. Subsequently, a method for systematic mapping of viral genomes will be developed utilizing single-stranded restriction fragments derivatized with the gene blocking agents. These derivatized fragments will be used for blocking specific sites on the genome being mapped. The effect of each of these blocks will be assessed by in vitro coupled transcription-translation of the blocked genomes. Compounds described herein should be valuable for in vitro studies of replication, repair, transcription, and translation. They should also enable systematic mapping and characterization of viral genomes. If in vivo applications prove feasible, the compounds will likely have important applications in the study of gene expression in procaryots and possibly eucaryots. Such agents may also prove valuable in combating viral infections, particularly latent infections and virally-mediated cancers.